Cruise control signal failure detecting system and method for automatic transmission

Abstract: In case where any of the conditions of (1) when the cruise control signal is erroneously turned on in case where a vehicle speed is smaller than a predetermined value (901), (2) when the cruise control signal which ought to be released is erroneously turned on at the time of turning a brake switch on (902), (3) when the cruise control signal is erroneously turned on in an "N" or "P" range (503), (4) when any of the paragraphs (1) to (3) is continued for a predetermined time (907), are satisfied, a failure of the cruise control set signal line (908) is detected, and the automatic transmission control of the cruise control is prohibited. The normal state is recovered when an off signal of the cruise control set is detected (904) in the above-described conditions. Accordingly, since a failure of the cruise control set signal line is reliably detected, the automatic transmission control is appropriately executed by using the cruise control signal. Thus, the automatic transmission control can be executed based on a cruise control signal.

Description: The present invention relates to a failure detecting system for an automatic transmission of a vehicle employing an engine rotational speed, a cruise control signal, a brake signal from a brake switch or a shift range switch operation signal from a shift range switch as one of control signals to control the automatic transmission. An automatic transmission AT is fundamentally controlled to be shifted by regulating depression of an accelerator pedal and a traveling speed of a vehicle. Accordingly, in case where the vehicle travels in a drive (D) range, reduction gears can be shifted by positively depressing or releasing the accelerator pedal. In a conventional automatic transmission, for example, in a drive (D) range, an optimum gear is selectively controlled from a vehicle speed at that time and a throttle opening according to a shift map storing a predetermined shift schedule as shown in Fig. 6. As a lockup function of an automatic transmission a lockup clutch is engaged when a vehicle speed becomes higher than a predetermined value in a certain gear position such as, for example, in a third gear or an overdrive (fourth gear), to directly couple an output shaft of a torque converter to an output shaft of an engine. In other cases, the lockup clutch is released to connect the input shaft of the torque converter to the output shaft of the engine. The lockup is released to utilize a function of the torque converter thereby to achieve smooth starting, smooth accelerating or smooth speed shifting without engine knocking or stop at the time of starting, abruptly accelerating, speed shifting the vehicle. However, in a state that a load is low and an engine rotational speed is high, the torque converter is locked up thereby to prevent loss of power due to a slip of the torque converter and hence to prevent a increase in fuel consumption. A cruise control unit so controls an opening of a throttle valve as to maintain a certain vehicle speed set by a driver as a desired traveling speed thereby controlling in response to a road state. As the typical automatic transmission control to execute as described above, JP-U-63-115558 discloses an internal combustion engine with an abnormality detector for judging an abnormality based on a rotational speed signal from a rotation detector for electrically detecting a rotational speed of the internal combustion engine and a fuel amount signal from a fuel amount detector for detecting a fuel supply amount to the internal combustion engine. In the above-described internal combustion engine with the abnormality detector, it is determined that an engine rotational speed signal line is on when an engine rotational speed is smaller than a predetermined value at a certain vehicle speed or more. However, even if an engine stop occurs at a certain vehicle speed or more, it is erroneously detected that the failure occurs at the engine rotational speed signal line. In such a case, it becomes impossible to detect a failure of an ignition pulse generating an engine rotational speed detection signal to be supplied to the engine rotational speed signal line. Furthermore, there are disadvantages that the automatic transmission control based on the engine rotational speed such as, for example, a gear shift control, a lockup control, a line pressure control can not be appropriately controlled. As the typical automatic transmission control to execute as described above, JP-U-63-137038 discloses an automatic transmission controller in which hunting of the vehicle speed due to a gear shifting during a cruise control traveling is prevented and a fail-safe control is performed when an abnormality of an automatic transmission occurs. More specifically, the automatic transmission controller additionally provides a memory map storing a shift schedule for controlling the automatic transmission in response to a cruise control signal supplied from a cruise controller, in which map a hysteresis width is so set as to reduce the number of repetitions of down and up shifting. In this case, since the number of times of gear shifting during the cruise control is reduced, hunching of the vehicle speed due to the gear shifting can be prevented, and a riding comfort can be improved. In the conventional automatic transmission controller as described above, a vehicle can be traveled smoothly without shock in the case of shifting gear during the cruise control, but it does not have a fail-safe function in case where the cruise control signal is, for example, erroneously generated even though the cruise control is not performed by the cruise controller. Usually, the automatic transmission controller functions as a gear shifting control, a lockup control, an overrunning clutch control (namely, engine brake control), etc. Therefore, if a fail-safe function is not provided, these functions are erroneously operated when a cruise control signal is erroneously generated. In a conventional automatic transmission, for example, in a drive (D) range, an optimum gear is selected based on a vehicle speed and a throttle opening at that time, from a shift schedule map storing a predetermined shift schedule as shown in Fig. 6. Further, in such an automatic transmission control, detection signals from various detecting sensors are input to a controller to perform a lockup control, an overrunning clutch control, a line pressure control, an auto-pattern select control, a gear shift timing control, a transfer clutch control of four-wheel drive as well as the above-described gear shift control. JP-A-1-145234 discloses a cruise control of a vehicle using a brake switch signal. Furthermore, JP-A-63-34349 discloses a method for detecting a trouble of a gear position switch. That is, if a gear position switch does not generate an ON signal when a predetermined time is elapsed after a gear shifting is performed, it is returned to a position before the gear changing, and when the same operation as above is conducted predetermined times or more, the switch is decided to be a trouble. However, in the above-described conventional method for detecting the trouble of the gear position switch, in case where the ON signal is not generated from the gear position switch, the gear is returned to the position before the gear shifting, and when the same operation as above is again conducted predetermined times or more, the switch is decided to be the trouble. Therefore, in the case of the trouble, it merely controls to return the position of the switch to the position before the gear shifting, an accurate automatic transmission control responsive to various traveling states of the vehicle is impossible. In US-A-5 157 990 a system for controlling an automotive power transmission is disclosed comprising a first input terminal for receiving a signal of a single switch and a second input terminal for receiving a signal of a vehicle speed sensor. The single switch turns on either a self diagnosis of the control unit or a cruise speed control. Therefore the control unit determines that the signal supplied to the first input terminal is a signal to turn on the self diagnosis when a vehicle speed sensor becomes abnormal and/or the vehicle speed is below 30 km/h. In case the vehicle speed sensor operates normal and the vehicle speed is above 30km/h the signal supplied to the input terminal of the control unit is determined to be a signal that the switch for the automatic cruise speed control device is turned on so that a control of the automatic cruise speed control device may be is performed normally. In US-A-5 058 698 a cruise control system for an automotive vehicle with an automatic transmission is disclosed, wherein said cruise control system cannot be activated when a transmission is set in a certain mode. The system comprises sensor means for monitoring the actual speed of the vehicle and to produce a first signal. Further the system comprises speed setting means for allowing manual setting of a desired vehicle speed and to produce a second signal. Actuator means actuate a mechanism which varies the vehicle speed, wherein control means control the actuator means based on the first and second signal to adjust the vehicle speed to the set speed. Inhibition means inhibit the control means from controlling the actuator means when the automatic transmission is set in a mode other than the drive mode. In US-A-5 074 371 a system and method according to the preamble of claim 1 or 2 for automatically controlling a vehicle speed to a desired cruise speed by means of an automatic (vehicle) speed control device (ASCD) is disclosed in which a torque converter and an automatic transmission are mounted. When a first predetermined degree of deviation of a present vehicle speed from a desired cruise speed is reached, the look-up state of a look-up device in this torque converter is inhibited. When the deviation further reaches a second predetermined deviation, being greater than the first, the automatic transmission is operated to inhibit a maximum speed gear range. An object of the present invention is to provide a failure detecting system for a cruise control set signal line connected to a controller for an automatic transmission of a vehicle which can reliably detect a failure of a cruise control set signal line thereby to appropriately control an operation of an automatic transmission control in response to a cruise control signal. This object is achieved with the features of the claims. According to the failure detecting system for the cruise control set signal line of the present invention, the automatic transmission control of the automatic transmission AT is prohibited in case where one of the following conditions is satisfied. More specifically, (1) When the cruise control signal is erroneously turned on in case where a vehicle speed is smaller than a value under which the operation of a cruise control is not performed. (2) When the cruise control signal which ought to be released is erroneously turned on at the time of turning a brake switch on. (3) When the cruise control signal is erroneously turned on in an "N" or "P" range. (4) When any of the paragraphs (1) to (3) is continued for a predetermined time. In case where any of the above conditions (1) to (4) is satisfied, it is determined that a failure occurs on the cruise control set signal line, whereby the automatic transmission control at the time of the cruise control is prohibited. However, a normal state is recovered when an off signal of the cruise control is detected after one of the above-described conditions is satisfied. The nature, utility, and further features of this invention will be understood from the following detailed description with respect to preferred embodiments of the invention by referring the accompanying drawings, briefly described below. In the accompanying drawings: Fig. 1 is a block diagram showing a failure detecting system for an automatic transmission of a vehicle employing an engine rotational speed according to an embodiment of the present invention; Fig. 2 is a flow chart for explaining an example of the operation of a failure detection system for a cruise control signal line according to Fig. 1; Fig. 3 is a flow chart for explaining an example of the operation of a failure detection system for a cruise control signal line according to Fig. 1; Fig. 4 is a flowchart for explaining an example of the operation of a failure detection system for a cruise control signal line according to Fig. 1; Fig. 5 is a flow chart for explaining an example of the operation of a failure detection system for a cruise control signal line according to Fig. 1; Fig. 6 is a view showing a shift schedule stored in a gear shift map for a conventional automatic transmission control; The embodiment of the present invention will be explained with reference to accompanying drawings. Fig. 1 shows a control system according to an embodiment of a failure detecting system for an automatic transmission of a vehicle of the present invention. The control system employs an engine rotational speed as one of input signals to control the automatic transmission. A failure is detected on the engine rotational speed when conditions to be described later are satisfied. When the failure is detected, a transmission control based on the engine rotational speed is prohibited, and a state before the failure is detected is maintained. The controls based on the engine rotational speed includes, for example, a gear shift control, a lockup control, and a line pressure control. A throttle opening detection signal from a throttle sensor 11 and an ATF oil temperature detection signal from an ATF temperature sensor 12 are input to an input interface circuit 21 of an electronic control unit (ECU) 20 of the control system. The throttle opening detection signal from the throttle sensor 11 is used to determine a gear shifting point, a line pressure in a control circuit of the automatic transmission and a lockup vehicle speed for the lockup. The ATF oil temperature detection signal from the ATF temperature sensor 12 is used to prohibit lockup at the time of a low temperature and to release a fourth gear. Various detection signals input through the input interface circuit 21 are converted to digital signals through an A/D converter 22, and then fed to a CPU 24. A program for executing a predetermined calculation of the CPU 24 is stored in a memory 24a associated with the CPU 24. A vehicle speed detection signal from a vehicle speed sensor 13, an engine rotational speed detection signal from an ignition pulse generator 14, a shift range signal from an inhibitor switch 14, and a throttle full close state detection signal from an idle switch 16, an ABS signal from an ABS control unit 19a, a cruise control signal from a cruise control unit, and a brake switch signal from a brake switch 19 are input to an input interface circuit 23. The vehicle speed detection signal from the vehicle speed sensor 13 is used to control a gear shifting, lockup, line pressure and transfer. The engine rotational speed detection signal from the ignition pulse generator 14 is used to smoothly control the lockup operation and to prevent overrunning of an engine in a "1", "2" or or "3" range. The shift range signal from the inhibitor switch 15 is used to determine the line pressure. The throttle full close state detection signal from the idle switch 16 is used to release a lockup clutch and to control the line pressure. An output of the CPU 24 is applied to an output interface circuit 25 for controlling ON/OFF of shift solenoids (1)31, (2)32, (3)33 and an output interface circuit 26 for controlling duty ratios of duty solenoids (A)34, (B)35 and (C)36. The shift solenoids (1)31, (2)32 control gear shifting, especially, its timing, thereby reducing a gear shifting shock. The shift solenoid (3)33 controls an overrunning clutch and a timing of shifting from a third gear to a second gear. The timing control reduces a shock at the time of shifting down the speed, and the overrunning clutch is operated at the time of decelerating, thereby effecting an engine brake. The duty solenoid (A) 34 regulates the line pressure to an optimum pressure responsive to a driving state. The duty solenoid (B)35 smoothly engages or disengages the lockup clutch. The duty solenoid (C)36 regulates a hydraulic oil pressure of a transfer clutch to control the rear wheel drive force. An embodiment of the present invention will be explained in detail with reference to Figs. 2 to 5. Referring back to Fig. 1, showing a control system including a failure detecting system for a cruise control set signal line connected to an automatic transmission of a vehicle. The control system employs a cruise control signal from a cruise control unit 18 as one of input signals to control the automatic transmission. A failure on the cruise control set signal line is determined when conditions to be described later are satisfied. When the failure is detected, a transmission control based on a cruise control signal is prohibited. However, a normal state is recovered when an OFF signal of the cruise control is detected in the conditions to be described later. As the automatic transmission control in case where the cruise control signal from the cruise control unit is employed, there are a gear shifting control (control at the time of cruise control), a lockup control (ordinarily a lockup control), an overrunning clutch control (namely, engine brake control), etc. The operation of the failure detecting system for the cruise control set signal line connected to the automatic transmission control system described above will be explained by referring to Figs. 2 to 5. Fig. 2 shows a flow to determine a case where a cruise control signal is erroneously turned on at a vehicle speed or less when the cruise control is not operated. When a detection signal from the vehicle speed sensor 13 is input to the CPU 24 through an input interface circuit 23, whether or not it is smaller than a predetermined value is judged (in a step 601). In case where it is judged that the detection signal is not smaller than the predetermined value, a failure flag of the cruise control signal is cleared, and a timer is set to a predetermined time (in steps 602 and 603). On the contrary, in case where it is judged that the detection signal is smaller than the predetermined value, whether or not the cruise control signal is input is judged (in a step 604). In case where it is judged that the cruise control signal is input, a failure flag of the cruise control signal is set thereby to decide a failure (in a step 605). Fig. 3 shows a flow to determine a case where a cruise control signal which ought to be released when a brake switch is turned on is erroneously turned on. Whether or not the brake switch 19 is turned on is judged (in a step 701). In case where a brake ON signal from the brake switch 19 is not input, a failure flag of the cruise control signal is cleared, and a timer is set to a predetermined time (steps 702 and 703). Moreover, in case where the brake ON signal from the brake switch 19 is input, it is judged whether or not the cruise control signal is input is judged (in a step 704), while when it is judged that the cruise control signal is input, a failure flag of the cruise control signal is set to decide a failure (in a step 705). Fig. 4 shows a flow to determined a case where a cruise control signal is erroneously turned on in an "N" or "P" range. A neutral range (N) or a parking range (P) is judged based on a shift range signal from the inhibitor switch 15 (in a step 801). As a result of the judgement, in case it is judged that the shift range signal does not indicate the neutral range (N) nor the parking range (P), a failure flag of the cruise control signal is cleared, and a timer is set to a predetermined time (in steps 802 and 803). On the contrary, in case where the neutral range (N) or the parking range (P) is detected in the step 801, whether the cruise control signal is input or not is judged (in a step 804). In case where the cruise control signal is input, a failure flag of the cruise control signal is set to judge the failure (in a step 805). Fig. 5 shows a flow to determine a case where any of when the cruise control signal is erroneously turned on at a vehicle speed or less in the case of cruise control non-operation, when the cruise control signal which ought to be released at the time of turning the brake switch on is erroneously turned on, and when the cruise control signal is erroneously turned on in an "N" or "P" range is continued for a predetermined time. First, when a detection signal from the vehicle speed sensor 13 is input to the CPU 24 through the input interface circuit 23, it is judged that the detection signal is smaller than a predetermined value or not (in the step 901). In case where the signal is judged not to be smaller than the predetermined value, whether or not the brake switch 19 is turned on is judge (in the step 902). In case where a brake ON signal from the brake switch 19 is not input, the neutral range (N) or the parking range (P) is judged based on a shift range signal from the inhibitor switch 15 (in the step 903). As a result of the judgement, in case where the signal is judged not to be the neutral range "N" nor the parking range "P", a failure flag of the cruise control signal is cleared, and a timer is set to a predetermined time (in steps 904 and 905). Moreover, when the vehicle speed is not smaller than the predetermined value (in the step 901), when the brake ON signal is detected (in the step 902), or further when either of the neutral range (N) and the parking range (P) is detected (in the step 903), whether or not the cruise control signal is input is judged (in a step 906). If the cruise control signal is not input, the flow is advanced to the step 904, and the failure flag is cleared. However, in case where the cruise control signal is input, whether the timer becomes "zero" or not is judged (in a step 907). That is, the "zero" of the timer means that the predetermined time is elapsed. In case where the timer becomes "zero", the failure flag of the cruise control signal is set to decide the failure (in a step 908). Summary of the conditions for detecting the failure of the cruise control set signal line is as follows. (1) When the cruise control is not operated, the cruise control signal is erroneously turned on in case where a vehicle speed is smaller than a predetermined value. (2) When a brake switch is turned on, the cruise control signal which ought to be released is erroneously turned on. (3) When an "N" or "P" range, the cruise control signal is erroneously turned on. (4) Any of the conditions (1) to (3) is continued for a predetermined time. In case where any of the above conditions (1) to (4) is satisfied, a failure on the cruise control set signal line is detected, the automatic transmission control based on the cruise control signal is prohibited. In the embodiment described above, a normal state is recovered when an OFF signal of the cruise control is detected after one of the above-described conditions is satisfied. Accordingly, since a failure of the cruise control set signal line is reliably detected, the automatic transmission control using the cruise control signal is appropriately executed.

Claims: A failure detecting system for an automatic transmission of a vehicle employing a cruise control signal as one of control signals to control said automatic transmission, the system comprising: vehicle speed detecting means (13) for detecting a vehicle speed; cruise control signal generating means (18) for generating a cruise control signal so as to instruct a cruise control to said automatic transmission; and transmission control prohibiting means for prohibiting a transmission control, characterized in that said transmission control is based on said cruise control signal, when said vehicle speed detected by said vehicle speed detecting means (13) is smaller than a predetermined value below which said cruise control is prohibited, and when said cruise control signal is generated from said cruise control signal generating mean (18) for a predetermined time. A method for detecting a failure of an automatic transmission for a vehicle employing a cruise control signal as one of control signals to control said automatic transmission, comprising the steps of: detecting a vehicle speed; generating a cruise control signal so as to instruct a cruise control to said automatic transmission; and prohibiting a transmission control, characterized in that said transmission control is based on said cruise control signal, when said detected vehicle speed is smaller than a predetermined value below which said cruise control is prohibited, and when said cruise control signal is generated for a predetermined time. The method according to claim 2, wherein said transmission control based on said cruise control signal is prohibited, when said vehicle speed is smaller than a predetermined speed below which said cruise control is prohibited, and when said cruise control signal is generated for a predetermined time.

Inventors: SAKAKIYAMA RYUZO, SHIRAKAWA KIMINAGA, TEZUKA KAZUNARI, SAKAKIYAMA, RYUZO, SHIRAKAWA, KIMINAGA, TEZUKA, KAZUNARI
Applicants: FUJI HEAVY IND LTD, FUJI JUKOGYO KABUSHIKI KAISHA
Application year: 1994
Main classification: F16H61
IPC codes: B60K31, F16H61, F16H59, F16H63, B60T17, B60W50